Antenna self-test systems

ABSTRACT

An antenna system is provided, in which a small test probe positioned in the antenna cavity is coupled to a system self-test unit. A signal, designed to exercise the primary functions of the system under evaluation is transmitted between the antenna and the test probe and then conducted to the actual system or the self-test unit for processing. This signal activates the appropriate system which is then evaluated for actual performance.

United States Patent Robbins et al.

[451 Oct. 10, 1972 ANTENNA SELF-TEST SYSTEMS Inventors: Robert Robbins,Hudson; Arthur R. I

Whitty, Hollis; Louis J. Kachavos, Derry, all of NH.

Sanders Associates, Inc., Nashua, NH.

Filed: Oct. 17, 1969 Appl. No.: 867,245

Assignee:

US. Cl. ..325/67, 325/133, 325/363 Int. Cl. ..H04b l/16, H04b l/04 Fieldof Search ..325/67, 133, 363; 343/l7.7,

References Cited UNITED STATES PATENTS 9/1964 Kishinsky ....325/67 IPrimary Examiner-Robert L. Griffin Assistant Examiner-Kenneth W.Weinstein Att0meyLouis Etlinger [5 7] ABSTRACT 4 Claims, 8 DrawingFigures I I I25; I3 I I I TRANSMITTER I T I L7 I I TEST I 29 SYSTEM HUNIT OPERATIONAL I I I INDICATOR is I a I I I I RECEIVER TEST I resr I ICONTROL I UNIT SELECTOR 20 I I L 1 w TRANSMITTER SYSTE M SYSTEMPATENTEDDBT 10 I972 SHEET 2 0F 6 IRNN J /NVEN7'0/?5 ROBERT ROBBiNSARTHUR R. WHITTY LOUIS J. KACH VOS FE: SM; 523% 292222228 ATTORNEYANTENNA SELF-TEST SYSTEMS FIELD OF THE INVENTION The present inventionrelates to electronic systems and their associated self-test units, moreparticularly, to self-test units designed to evaluate the performance ofan antenna, its interconnecting cables, and the associated electricalcomponents.

.PRIOR ART In the field of airborne electronic systems, moreparticularly, the system comprising the antenna interconnecting cables,and electrical components, it is recognized that it is extremelydifficult, if not impossible to test these units while the aircraft isin actual flight. For example, some systems such as navigational or VORequipment can be tested in flight by tuning the receiver to receivespecial test signals transmitted at preselected ground stations.However, only a limited number of test stations are strategicallylocated in the United States for reasons such as, cost, and these are inor near the major airway lanes. Since many aircraft operate in otherareas, these test centers are not available to all aircraft.

Other airborne electronic systems provide self-test features in only theelectrical equipment. In particular, these self-test features onlyprovide the means to test the electronic component section of thesystem, and not the total system which includes the antenna andinterconnecting cable paths.

Further, the function of some electronic systems in certain aircraft isclassified, such as for security reasons. For example, the function ofcertain electronic systems in military aircraft must necessarily besecret and therefore classified. In these instances, it is impossible toprovide ground test stations, and the available electronic self-testsystems do not satisfy the requirements of determining the operationalstatus of the total electronic system. I

An alternative available solution is to use ground support testequipment, similar in design and function to the self-test features usedin the airborne equipment test procedures. The equipment used in theseprocedures provides'a system .of signals designed to check out thefunction of the particular electronic systems. However, similar to theabove-described airborne self-test features, only the active electroniccomponents of the system are evaluated for system performance since thetest signals are inserted through electrical connections provided in thesurface of the airplane. Thus the antenna and interconnecting cable runsare not used or evaluated in these tests. Further, there is no way tocheck out or evaluate the total electronic system after the airplane isairborne.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of thisinvention to provide a novel and improved test system;

An additional object of this invention is to provide an antenna systemin which a test probe is contained within the antenna cavity;

It is a further object of this invention to provide a system self-testunit which is capable of producing test signals which will exercise theprimary functions of the total airborne electronic systems;

A further object of this invention is to transmit the simulated testsignal from the test probe to the system antenna, and then to the systemwhich is to ,be evaluated for operational status;

Another important object of this invention is to provide a systemself-test unit which will evaluate the operational effectiveness of theantenna, the interconnecting cables and the electronic systems while theairplane is in flight.

According to this invention, this and other objects which will becomeapparent upon reading the specification are embodied in apparatuscomprising an antenna system which includes a test probe within theantenna cavity, the test probe is capable of transmitting to orreceiving from the main system antenna a signal which will exercise theprimary functions of the electronics system. The signal activates thesystem to be evaluated and the response of the interrogated system isthen evaluated for performance.

BRIEF DESCRIPTION OF THE DRAWINGS For a clearer understanding of theinvention, reference may be made to the following detailed descriptionand accompanying drawings, in which:

FIG. 1 is a schematic representation of theoperational electronic systemto be evaluated and its associated self-test unit and antenna testprobe;

FIG. 2 is a schematic representation of the communications andnavigational systems and the associated DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENTS An operational system embodying the invention isillustrated in FIGS. 1, 2, 4, 5, and 6 and includes the operationalelectronics system being evaluated 36, an antenna compartment 11including an antenna 12 and an antenna test probe 13, a self-test unit18 and a local control unit 27. When a test control selector 28 isenergized, a simulated, operational signal which will exercise theprimary functions of the airborne electronics is transmitted between theantenna 12 and the antenna test probe 13, that is, the signal isradiated from one of the antennas. This signal is then conducted byconducting wire 16 or 15 to be processed in either the self-test unit 18or the operational system 36 respectively and evaluated. If the totalsystem performs satisfactorily, more particularly, the antenna 12, thesystem 36 and the interconnecting conducting wire 1 5, an appropriatesignal indicating system performance is transmitted to an indicator 29on the test control console.

actual or simulated, must be transmitted from or received at the systemantenna 12. More particularly, when the transmitter system 37 is beingtested, an actual system signal is conducted through conducting wire 15to antenna 12 transmitted and received at test probe 13, and thenprocessed by the transmitter test unit 19. Alternatively, when thereceiver unit 38 is to be tested, antenna 12 receives a simulated signalfrom t test probe 13. The simulated signal generated in receiver testunit 20 is-conducted through conducting wire 16 to probe 13. Thissimulated signal is processed by receiver unit 38 and the resultsthereof are evaluated.

An important feature of this invention is the proximity of antenna 12and antenna test probe 13. More particularly, the antennas arepositioned so that a signal transmitted from one antenna will bereceived at the other antenna, that is, they are in each othersradiation pattern. In the system described in this specification, aflush mount antenna system, antenna 12 and test probe 13 are positionedwithin the antenna compartment 11 or cavity. This system, however, mayalso be used with external mounted antenna systems. The only criteriabeing the need for the close proximity of the antenna 12 and its antennatest probe 13. Furthermore, self-test unit 18 may also be physicallylocated within the antenna compartment 1 l, as well as elsewhere withinthe aircraft structure. Q

The antennatest probe 13 is any device that is capable of transmittingand receiving a signal. In effect it is an antenna having sufficientsensitivity to transmit and receive an intelligible signal.

In describing the operation of the preferred system, the operation ofthe transmitter self-test system will first be discussed. Normally, theairborne electronics system 36 is functioning at all times and thesystem selftest unit 18 is energized whenever the system 36 is to betested. Thus, in order to test and evaluate transmitter unit 37 of thesystem 36, it is necessary to transmit from antenna 12 a signalgenerated by transmitter unit 37. At the same time, test controlselector 28 is energized and thereby permitting a signal being receivedat test probe 13 to be processed by the transmitter test unit 19. If theappropriate transmitted signal is detected and processed by transmittertest unit 19, a signal is displayed at systems operational indicator 29.Conversely,

a if an incorrect signal is being transmitted from antenna 12, then nosignal is given at system indicator unit 29.

To test the receiver portion of the unit under test, receiver unit 38,test control selector 28 is switched on thereby energizing receiver testunit 20. Receiver test unit 20 generates a test signal which is designedto test the primary functions of receiver unit 38; that is, thissimulated signal is equivalent to the signal normally received andprocessed by receiver unit 38. Also, this signal may be designed so thatreceiver unit 38 will respond in a predetermined manner; such as to emitan audible tone or cause a predetermined meter indication or reading.This signal is conducted by conducting wire 16 to test probe 13;transmitted to antenna 12 and conducted to and processed by receiverunit 38. If the predetermined result is detected, the pilot then knowsthat this particular system is functioning properly.

The system indicator 29, illustrated in FIG. 1, is connected to both theoperational test system 36 and the self-test unit 18. in the examplesset forth in the specification, the system indicator 29 associated withthe receiver unit 38 is the indicator within the receiving unit that isused during actual system operation; such as, a speaker unit for thecommunication system, a range meter in the distance measuring equipmentor lights in the marker beacon system. The system indicator 29associated with the transmitter test unit is any indicating deviceinterconnected with test unit 19; such as, an audible sound device, alight source or a calibrated meter. In effect, system indicator29 is agono-go device, and may be designed to give a signal for either anoperational or non-operational system.

The test control selector 28, illustrated in FIG. 1, is connected toboth the operational test system 36 and the self-test unit 18. In thesystem actually constructed in accordance with the principles of thisinvention, test control selector 28 is only interconnected with andenergizes self-test unit 18. System 36 is made operational for testpurposes in the same manner as when the system is in actual use.Further, the local control unit 27, as constructed, comprises a testselector 28 for each self-test unit. However, other types of controlunits may be used, for example, a multiposition switch used inconjunction with a test selector 28. In this example, the switch ispositioned to test a particular system, activation of test selector 28will energize selftest unit 18. In this manner, a common test selector28 is shared between all of the self-test systems.

The power level of the simulated test signal, through proper designtechniques, is only sufficient to be received by antenna 12 andprocessed by the equipment in system 36. Conversely, the power level ofthe signal is insufficient to be transmitted into free space and bedetected so as to activate any corresponding equipment at other places.

An important design consideration is the effective isolation of theself-test unit 18 and the test probe 13 so that they will not berendered inoperative by the high RF transmitter power emitted fromantenna 12.

In a specific embodiment of the invention, illustrated in FIGS. 2 and3A-3C, the self-test system 18 is designed to test the navigational 40and communication 39 equipment in the aircraft. The communication 39 andnavigational 40 equipment being the conventional equipment that isavailable in the commercial market.

The communication equipment 39 contains both a transmitter and areceiver section, with both sections to be tested on an individualbasis. The communications transmitter test unit 21, illustrated in FIG.2 and FIG. 3A, comprises a coupling circuit 70, a broadband detectorcircuit 71, an amplifier 72 and an indicator means 31 such as a light, ameter or other signaling device.

To test the transmitter section of the communication equipment 39 thepilot places the transmitter section of equipment 39 in the transmitmode and places the test control selector means 30 in the test mode,thereby energizing the transmitter test unit 21. A normal system signal,in particular, the if carrier signal, is then conducted from thetransmitter section through conducting wire 15 to the antenna 12, andtransmitted into free space. The transmitted signal is then received bythe test probe 13 and conducted through conducting wire 16 to thetransmitter test unit 21. The received signal is then coupled throughcoupling network 70 to the broadband detector circuit 71. The detectedsignal is amplified in amplifier 72 and transmitted to indicator means31 at the local control unit 27. Indicator means 31 may be any devicewhich will produce a detectable signal in response to a signal fromamplifier 72, such as a light or a meter. The meter may be calibrated toindicate the signal strength of the transmitted signal. If thetransmitted section of the communications unit 39 is not operatingproperly, the test unit 21 will not process a properv signal, andindicator means 31 will not be energized.

The receiver test unit 22 section of the communications unit 39,illustrated in FIGS. 2 and 3B, includes a signal generator 75 a sweepdriver circuit 76 and a sweep oscillator unit 77.

To test the receiver section of the communications system 39, the pilotplaces the receiver test control selector 32 in the test mode, and thereceiver section of system 39 in the receive mode. Upon energization ofreceiver test unit 22, the signal generator 75 applies a low frequencysignal to sweep driver circuit 76. The output of the sweep drivercircuit 76 is designed to vary at an audio rate, such as l KI-Iz. Theoutput of the sweep circuit 76 modulates thesignal developed inoscillator unit 77, and the output signal of the oscillator unit 77 thenvaries between two predetermined frequencies. The output signal isconducted to test probe 13 through conducting wire 16. The range of thisswept frequency signal transmitted signal is set to encompass allfrequency bands in which the communications receiver may be tuned. Ifthe total receiver section of the communications system is operatingproperly, an audio tone will be generated as the swept frequency passesthrough the particular frequency band in which the communicationsreceiver is tuned. Conversely, if no audio tone is present, the systemis not operating satisfactorily.

The navigational self-test unit 23, illustrated in FIGS. 2 and 3Ccomprises a low frequency oscillator 80, a phase adjuster 81, anoscillator 82, a differential amplifier 83 and a VHF oscillator 84.

To test the navigational equipment 40, the self-test control means 33 isplaced in the test position thereby energizing the self-test unit 23.The self-test unit 23 may be designed to give any reading on thenavigational (VOR) indicator, such as zero or 180. When the self-testunit 23 is energized, two signals are generated, a first signal beingsupplied by LF oscillator 80, set-at 30Hz, and a second signal inoscillator 82, set for 9960 Hz. The first signal, 80, modulates thesecond signal produced by oscillator 82 after passing through phaseadjuster 81. In this particular instance, phase adjuster 81 varies thephase of the signal from oscillator 82 so that it has a certain phaserelationship with the first signal generated in LF oscillator 80 toproduce a desired reading on the VCR indicator. The frequency modulatedsignal from oscillator 82 is applied to one input terminal ofdifferential amplifier 83 and a second signal from oscillator 80 isapplied to the other input terminal of amplifier 83. Phase network 81shifts the phase of the first low frequency signal so'that the modulatedoutput signal from oscillator 82 is either in phase (0) or out of phase(180) with the first low frequency signal appearing'at the input ofamplifier 83. The signal of the VHF oscillator is then frequencymodulated by the combined or mixed signal from amplifier 83, and theresultant signal is conducted through conducting wire 16 to test probe13. Navigational antenna 12 then receives the signal transmitted fromprobe 13 which is then conducted to and processed by the navigationalequipment 40. As previously stated, the navigational self-test unit maybe designed so that either a 0 or a 180 indication is produced on thenavigational (VOR) indicator. Then any deviation from these readingswould indicate the amount of error in the indicator system or thenavigational (VOR) system.

A third specific embodiment of this invention, illustrated in FIG. 4, isthe self-test system for the distance measuring equipment 41(hereinafter referred to as DME). The self-test system comprises a DMEself-test unit 24, a test control selector 34, and coupling element 93for coupling a simulated signal onto conductor 15 which causes theairborne DME 41 to provide a predetermined indication.

The DME self-test unit 24 comprises an rf detector unit 89, pulsediscriminator circuits 88, an amplifier 90, a delay line unit 91, anoscillator-modulator circuit 92, and a time control unit 87.

In actual operation the airborne unit transmits a twopulse group signalto a fixed ground station. Each pair of signals received at a groundstation is detected, amplified and then delayed for an accuratelycalibrated period. The delayed signal thereafter triggers a modulatorcircuit transmitting a pulse group back to the airplane, and indicatingcircuits within the DME 41 detect and measure the transit time of thepulse groups thereby providing an indication of distance from the groundstation. The DME self-test unit 14 is designed to operate in a similarmanner and provide pulses that indicate a predetermined distance.

When the DME test control selector 34 is placed in the test position,time control unit 87 is energized for a preselected length of time, andwhich simultaneously energizes the pulse discriminator circuits 88 for acorresponding length of time. During this time period, the transmitterunit of the DME 41 supplies rf power containing groups of pulse-pairsignals to antenna 12. The transmitted groups of pulse-pair signals arereceived by test probe 13, coupled to and detected within detector unit89, and then applied to the pulse discriminator circuits 88. If, andonly if, both pulse pairs are present and separated by a predeterminedgiven pulse length will the pulse discriminator circuit 88 couple thesignal containing the pulse pair to amplifier circuit 90. Amplifiercircuit 90 reconstructs the pulse pair signal and applies them to delayline unit 91. After a calibrated length of time the pulse-pair ofsignals modulate a high frequency signal developed in oscillation unit92. This modulated signal is then coupled to conducting wire 15 throughcoupling unit 93 and applied to the receiver circuit of the DME 41. Thereceiver portion of the DME 41 detects and measures the time lapse ofthe transmitted pulse-pair signals and provides a signal to give anindication on the DME range meter. As previ ously stated, the reading onthe DME range meter is determined by the length of time delay withinunit 91.

It is thus seen that the DME self-test unit performs a system check onthe entire avionic system in the airplane; that is, the DME 41,conducting cable and its couplings and the DME antenna 12.

A fourth specific embodiment of this invention, illustrated in FIG. 5,is the self-test system for the transponder equipment 42, and comprisesa self-test unit 25, a local control unit 27, an antenna test probe 13,and a signal coupling network 101. The self-test unit is designed tosimulate the operation performed by a ground station; that is, byapplying an interrogating signal to the transponder equipment and thenanalyzing the signals that are retransmitted by the transponderequipment 42.

To test the transponder equipment 42, the test control selector isplaced in the test position, and power is applied to the transponderself-test unit 25. Initially, a clock circuit 98 applies a series ofregulated pulses to a delay unit 99. The delay unit 99 is designed toarrange this series of pulses into a train of pulses according to apredetermined code. The signals from the delay line 99 are applied tooscillator unit 100 to modulate the signal developed therein. Themodulated output signal from oscillator unit 100 is then coupled toconducting line 15 through coupling circuit 101. This modulated signalis then received at and processed in the receiver portion of thetransponder equipment 42. The coupling circuit 101 is designed toisolate the antenna 12 from any signal generated in the self-test unit25, and to direct all signals to the transponder equipment 42.Therefore, the simulated test signal will not transmit from antenna 12and prevent the possibility of energizing other equipment. The receivingportion of the transponder equipment 42 processes the simulated signaland the interrogation network therein generates a signal in the form ofa coded pulse train which is transmitted by antenna 12. A detectioncircuit 95 detects the reply code signal received at probe 13, andconducts the signal to a pulse discrimination circuit 96. If the pulsediscrimination circuit 96 detects the appropriate time interval betweenpulses in the code pulse train, an output signal is applied to thecoincidence detector circuit 97. The coincidence detector circuit 97being energized for a limited length of time, controlled by test controlselector 35, then applies a signal to test indicator means 50. If anyone component within the entire transponder system is non-operational,the indicator means 50 willnot receive a signal.

A fifth specific embodiment of this invention, illustrated in FIG. 6, isthe self-test system for the marker beacon system 43, and comprises aself-test unit 26, a local control unit 27, and an antenna test probe13. The self-test unit is designed to simulate the functions performedby the ground stations, more particularly, to amplitude modulate acarrier frequency with three different frequencies to check out thereceiver portion ,of the marker beacon system.

To test the marker beacon equipment 43, test control selector 51 isplaced in the test position, and power is applied to the marker beaconself-test unit 26. The test control selector 51 is designed to activateoscillators 61, 62, and 63 individually, not together. For example, thetest control selector 51 may be three individual switches or amultiposition switch. The output signal from oscillator 61 amplitudemodulates the carrier signal generated in oscillator 64. This amplitudemodulated signal is then transmitted from the test probe 13 to antenna12 and conducted through conducting wire 15 to the marker beacon system43. The carrier frequency signal is removed in the receiver section, andthe frequency of the remaining signal, equivalent to that of oscillator61, is passed through one of three band pass filters and causes anappropriate indicator lamp to light up on the panel unit of the beaconsystem 43. Next, the output signal from oscillators 62 and 63individually modulate the oscillator signal of unit 64 and are processedby marker beacon system 43 respectively.

The actual frequencies developed by oscillators 61, 62, and 63 are 400,1,300 and 3,000 Hz respectively. Thus, since each signal is within theaudio range, means may be incorporated to provide an audible indicationof each of the individual test signals.

The foregoing description has dealt with specific communication andnavigational systems. Nevertheless, by using this same principle, anysystem which transmits and/or receives a signal from an antenna mayincorporate this self-test system, and its associated test probeantenna. For example, an aircraft may employ various types of radarsystems with each having its own self-test system, or glide-slopereceiver systems.

The self-test system would employ an oscillator unit to produce a signalhaving the same frequency as that normally received by the radar system.In addition, the self-test unit would generate the information whichmust be contained in the signal received by the radar system, thisinformation being modulated on the oscillator signal. Also, theoscillator circuit would be designed only to operate during the periodswhen the transmitter section of the radar system is not supplying asignal to the radar antenna, that is, the transmitter on time. Thiscould be done by using appropriate timing signals received from thetransmitter section of the radar. Also, the oscillator circuit wouldhave to be protected from the energy contained in the transmitter pulseduring normal operation of the system.

The self-test systems set forth hereinabove have been described asdiscrete components. More particularly, each operational system has itsassociated self-test and test control units. It is to be understood,however, that the self-test unit and control unit may be designed to bean integral component of the particular avionic system. The function ofthe self-test unit would be similar to that described hereinabove. Also,all self-test units and control units may be combined into one self-testsystem wherein one would select the desired test to be performed, andthen energize the test control selector. Further, a programmable devicemay be associated with the test control units, the function of whichwould be to activate both the self-test unit and its associatedoperational system for test purposes. Also, this device may be designedto automatically test all systems in any given sequence, once the testselector is energized.

It is to be understood that the above-described ar' rangements are byway of illustration only and that the basic concepts of the self-testsystem may be used with any other type system which transmits and/orreceives a signal containing information required by the associatedprocessing equipment.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. A system for receiving energy, said system having a first receiverapparatus coupled to an antenna capable of radiating and receivingenergy, wherein the improvement comprises:

an antenna test probe capable of radiating and receiving energy, saidtest probe being positioned in close proximity to said antenna andwithinthe field of radiation of said antenna; test means adapted toapply a test signal having prearranged information to provide apredictable result to said test probe, said test means comprising asignal generator means arranged to generate a first signal having fixedfrequency, a sweep oscillator means arranged to receive said firstsignal and to generate a second signal which varies in frequency betweena third and a fourth frequency, and an oscillator means arranged togenerate a fifth signal having a sixth frequency, said oscillator meansadapted to receive said second signal and to modulate said fifth signalthereby to generate a seventh signal which varies in frequency betweenan eighth and ninth frequency, said eight frequency being less and saidninth frequency being greater than the frequency of said fifth signal,and circuit means arranged to couple said seventh signal to said testprobe, said first receiver apparatus to receive and process said testsignal; and

indication means responsive to the processing of said test signal toprovide an indication of the predictable result if said first receiverapparatus is functioning properly.

2. A system for receiving energy, 'said system having a receiverapparatus coupled to an antenna capable of radiating and receivingenergy, wherein the improvement comprises:

an antenna test probe capable of radiating and receiving energy,'saidtest probe being positioned in close proximity to said antenna andwithin the field of radiation of said antenna; test means arranged toapply a test signal having predetermined information to provide apredictable result to said test probe, said test means comprises asignal generating means arranged to provide a first signal having afirst fixed frequency to a variable phase shift means, said phaseshiftmeans arranged to vary the phase of said first signal;

second signal generating means arranged to generate a second signalhaving a secondfixed frequency which is greater than said first fixedfrequency, said second signal generating means arranged to receive saidfirst signal from said phase shifter and modulate said second signalthereby, the phase difference between said first signal and said secondsignal providing compass directional information, means for combiningsaid second signal with said first signal; and a third signal generatingmeans capable of producing a third signal having a third frequencygreater than said first or second frequency, said third signalgenerating means arranged to receive said combined signal and modulatesaid third signal thereby and apply said modulated signal to said testprobe, said modulated signal being said test signal, and said receiverapparatus to receive and process said test signal; and

indication means responsive to the processing of said test signal toprovide an indication of said predetermined compass directionalinformation if said receiver apparatus is functioning properly. 3. Asystem for transmitting and receiving energy for measuring the distancebetween the transmitting source and a fixed reference station, saidsystem having a first transmitter apparatus and first receiver apparatuswith said transmitter means arranged to transmit an r-f carrier signalmodulated by a first signal having prearranged pulse pattern formationfrom an antenna to a remote ground station and said receiver meansarranged to receive and process said first signal retransmitted fromsaid ground station, said receiver means capable of measuring the timeelapsed from the transmission to the reception of said first signalthereby providing an indication of the distance, said first transmitterand first receiver apparatus coupled to an antenna capable of radiatingand receiving energy, wherein the improvement comprises:

an antenna test probe capable of radiating and receiving energy; saidtest probe being positioned in close proximity to'said antenna andwithin the field of radiation of said antenna; test means arranged toreceive said r-f carrier modulated signal from said test probe, saidtest means having means to detect said first signal with saidprearranged pulse pattern, said detector means being arranged to couplesaid first signal to discrimination circuit means, said discriminationcircuit means being arranged to couple said first signal if said firstsignal comprises the prearranged pulse pattern formation to a delaymeans, said delay means couples said first signal to a signal generatingmeans after a predetermined length of time, said signal means generatingmeans having a frequency equal to the r-f carrier frequency, said signalgenerating means combining said first signal with said carrier frequencysignal, said signal generating means arranged to couple said combinedsignal to said distance measuring receiver-means for processing; and

indication means responsive to the processing of said combined signal toprovide an indication of said predetermined delay of said test means ifsaid distance measuring means is functioning properly. 4. A system fortransmitting and receiving energy, said system having a firsttransmitter and a first receiver apparatus coupled to an antenna capableof radiating and receiving energy, herein the improvement comprises:

an antenna test probe capable of radiating and receiving energy, saidtest probe being positioned in close proximity to said antenna andwithin the field of radiation of said antenna; test system coupled tosaid test probe, said test system having means to produce a first signalhaving a series of pulses, said first signal being coupled to a signaldelay means, said delay means being constructed so as to arrange saidseries of pulses in a predetermined time relationship, signal generatormeans arranged to produce a second signal having a frequency equal tothe r-f carrier frequency of a transponder apparatus, said signalgenerator means so constructed as to modulate said second signal withsaid first signal from said delay line, means for coupling saidmodulated signal to said transponder apparatus for processing;

said transponder apparatus comprising transmitter and receiver means,said receiver means arranged to receive said modulated signal and togenerate a response signal having a series of pulses, the timerelationship between said pulses being determined by the timerelationship between the pulses of said first signal from said delayline,

said transponder receiving means arranged to couple said response signalto said transponder transmitting means for transmission from saidantenna,

said test system arranged to receive said response signal from said testprobe, said test system further means so constructed 88 to produce anoutput signal if the predetermined time relationship between the pulsesof said response signal is present; and

indication means responsive to the processing ofsaid response signalhaving a series of pulses if said transponder apparatus is functioningproperly.

' IF l

1. A system for receiving energy, said system having a first receiverapparatus coupled to an antenna capable of radiating and receivingenergy, wherein the improvement comprises: an antenna test probe capableof radiating and receiving energy, said test probe being positioned inclose proximity to said antenna and within the field of radiation ofsaid antenna; test means adapted to apply a test signal havingprearranged information to provide a predictable result to said testprobe, said test means comprising a signal generator means arranged togenerate a first signal having fixed frequency, a sweep oscillator meansarranged to receive said first signal and to generate a second signalwhich varies in frequency between a third and a fourth frequency, and anoscillator means arranged to generate a fifth signal having a sixthfrequency, said oscillator means adapted to receive said second signaland to modulate said fifth signal thereby to generate a seventh signalwhich varies in frequency between an eighth and ninth frequency, saideight frequency being less and said ninth frequency being greater thanthe frequency of said fifth signal, and circuit means arranged to couplesaid seventh signal to said test probe, said first receiver apparatus toreceive and process said test signal; and indication means responsive tothe processing of said test signal to provide an indication of thepredictable result if said first receiver apparatus is functioningproperly.
 2. A system for receiving energy, said system having areceiver apparatus coupled to an antenna capable of radiating andreceiving energy, wherein the improvement comprises: an antenna testprobe capable of radiating and receiving energy, said test probe beingpositioned in close proximity to said antenna and within the field ofradiation of said antenna; test means arranged to apply a test signalhaving predetermined information to provide a predictable result to saidtest probe, said test means comprises a signal generating means arrangedto provide a first signal having a first fixed frequency to a variablephase shift means, said phase shift means arranged to vary the phase ofsaid first signal; a second signal generating means arranged to generatea second signal having a second fixed frequency which is greater thansaid first fixed frequency, said second signal generating means arrangedto receive said first signal from said phase shifter and modulate saidsecond signal thereby, the phase difference between said first signaland said second signal providing compass directional information, meansfor combining said second signal with said first signal; and a thirdsignal generating means capable of producing a third signal having athird frequency greater than said first or second frequency, said thirdsignal generating means arranged to receive said combined signal andmodulate said third signal thereby and apply said modulated signal tosaid test probe, said modulated signal being said test signal, and saidreceiver apparatus to receive and process said test signal; andindication means responsive to the processing of said test signal toprovide an indication of said predetermined compass directionalinformation if said receiver apparatus is functioning properly.
 3. Asystem for transmitting and receiving energy for measuring the distancebetween the transmitting source and a fixed reference station, saidsystem having a first transmitter apparatus and first receiver apparatuswith said transmitter means arranged to transmit an r-f carrier signalmodulated by a first signal having prearranged pulse pattern formationfrom an antenna to a remote ground station and said receiver meansarranged to receive and process said first signal retransmitted fromsaid ground station, said receiver means capable of measuring the timeelapsed from the transmission to the reception of said first signalthereby providing an indication of the distance, said first transmitterand first receiver apparatus coupled to an antenna capable of radiatingand receiving energy, wherein the improvement comPrises: an antenna testprobe capable of radiating and receiving energy; said test probe beingpositioned in close proximity to said antenna and within the field ofradiation of said antenna; test means arranged to receive said r-fcarrier modulated signal from said test probe, said test means havingmeans to detect said first signal with said prearranged pulse pattern,said detector means being arranged to couple said first signal todiscrimination circuit means, said discrimination circuit means beingarranged to couple said first signal if said first signal comprises theprearranged pulse pattern formation to a delay means, said delay meanscouples said first signal to a signal generating means after apredetermined length of time, said signal means generating means havinga frequency equal to the r-f carrier frequency, said signal generatingmeans combining said first signal with said carrier frequency signal,said signal generating means arranged to couple said combined signal tosaid distance measuring receiver means for processing; and indicationmeans responsive to the processing of said combined signal to provide anindication of said predetermined delay of said test means if saiddistance measuring means is functioning properly.
 4. A system fortransmitting and receiving energy, said system having a firsttransmitter and a first receiver apparatus coupled to an antenna capableof radiating and receiving energy, wherein the improvement comprises: anantenna test probe capable of radiating and receiving energy, said testprobe being positioned in close proximity to said antenna and within thefield of radiation of said antenna; a test system coupled to said testprobe, said test system having means to produce a first signal having aseries of pulses, said first signal being coupled to a signal delaymeans, said delay means being constructed so as to arrange said seriesof pulses in a predetermined time relationship, signal generator meansarranged to produce a second signal having a frequency equal to the r-fcarrier frequency of a transponder apparatus, said signal generatormeans so constructed as to modulate said second signal with said firstsignal from said delay line, means for coupling said modulated signal tosaid transponder apparatus for processing; said transponder apparatuscomprising transmitter and receiver means, said receiver means arrangedto receive said modulated signal and to generate a response signalhaving a series of pulses, the time relationship between said pulsesbeing determined by the time relationship between the pulses of saidfirst signal from said delay line, said transponder receiving meansarranged to couple said response signal to said transponder transmittingmeans for transmission from said antenna, said test system arranged toreceive said response signal from said test probe, said test systemfurther comprising signal detection means coupled to said antenna testprobe, said detection means so constructed as to produce a series ofpulses separated by a time relationship equal to the time relationshippresent in said transponder response signal, and discrimination circuitmeans arranged to receive said series of pulses, said discriminationmeans so constructed as to produce an output signal if the predeterminedtime relationship between the pulses of said response signal is present;and indication means responsive to the processing of said responsesignal having a series of pulses if said transponder apparatus isfunctioning properly.